An effective class of detergent-dispersants for lubricating oils taught in the prior art are the N-substituted alkenyl succinimides characterized by the formula: ##STR1## where R is alkenyl (monovalent, monoolefinic aliphatic hydrocarbon radical) of from 30 to 300 carbons and D is an amine radical selected from the group consisting of alkylene amino and polyalkylene polyamine. These prior nitrogenous dispersants are prepared by reacting polyalkene or halogenated polyalkene with maleic anhydride to form the alkenyl succinic anhydride followed by the direct reaction of the succinic anhydride with alkylene diamine or polyalkylene polyamine. The prior art succinimides, although effective detergent-dispersants are finding increasing difficulty in meeting the present day and future requirements in regard to preventing or inhibiting the formation of varnish in automotive engines.
In one effort to meet this varnish problem, the prior art, as represented by U.S. Pat. No. 3,620,977, developed a reaction product of halogenated succinyl lactone and a hydrocarbon amine by contacting alkenyl succinic anhydride with a halogen in the presence of hydroxylic compound such as water and methanol to form a halogenated succinyl lactone and then reacting this lactone with hydrocarbon amine to form a complex nitrogenous reaction product which is then subjected to a solvent extraction, e.g., methanol extraction to remove the undesired by-products. In the product defining procedure of the prior art, the hydroxylic compound is indicated to be essential.